Re: [Xen-devel] [PATCH v1 5/6] x86/vvmx: correctly report vvmcs size

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Sergey Dyasli [mailto:sergey.dyasli@xxxxxxxxxx]
> Sent: Friday, October 12, 2018 11:28 PM
> 
> The size of Xen's virtual vmcs region is 4096 bytes. Correctly report
> it to the guest in case when VMCS shadowing is not available instead of
> providing H/W value (which is usually smaller).

what is the problem of reporting smaller size even when actual
size is 4096? is L1 expected to access the portion beyond h/w
reported size?

> 
> Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
> ---
>  xen/arch/x86/hvm/vmx/vvmx.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/xen/arch/x86/hvm/vmx/vvmx.c
> b/xen/arch/x86/hvm/vmx/vvmx.c
> index 8b691bfc04..2c2ba36d94 100644
> --- a/xen/arch/x86/hvm/vmx/vvmx.c
> +++ b/xen/arch/x86/hvm/vmx/vvmx.c
> @@ -2064,6 +2064,14 @@ int nvmx_msr_read_intercept(unsigned int msr,
> u64 *msr_content)
>          data = (host_data & (~0ul << 32)) |
>                 (vmcs->vmcs_revision_id & 0x7fffffff);
>          unmap_domain_page(vmcs);
> +
> +        if ( !cpu_has_vmx_vmcs_shadowing )
> +        {
> +            /* Report vmcs_region_size as 4096 */
> +            data &= ~VMX_BASIC_VMCS_SIZE_MASK;
> +            data |= 1ULL << 44;
> +        }
> +
>          break;
>      }
>      case MSR_IA32_VMX_PINBASED_CTLS:
> --
> 2.17.1


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